The availability of radio communication systems through which to communicate is a necessary aspect for much of modern society. Many varied types of radio communication systems have been developed and used for various purposes. Cellular radio communication systems, for instance, have achieved significant levels of usage. Network infrastructures of cellular communication systems have been installed to encompass significant portions of populated areas of the world. Successive generations of cellular communication systems have been developed, and their network infrastructures deployed and installed. Early-generation cellular communication systems were used primarily for voice communications. Successor-generation systems provide increasingly for data communication services, including multi-media communication services.
A cellular communication system is generally a bandwidth-constrained system. That is to say, the radio-frequency bandwidth allocated to a cellular communication system is limited, and the limited bandwidth sometimes constrains the communication capacity of the system. Other radio communication systems are also similarly and also generally bandwidth constrained. Efforts are therefore made to make efficient use of the allocated bandwidth. And, communication schemes have been developed to make the most efficient possible use of bandwidth allocated to a communication system. For instance, OFDM (Orthogonal Frequency Division Multiplexing) schemes have been proposed and planned for use as part of a new-generation, cellular communication system. In an OFDM communication scheme, sub-carriers are defined. The sub-carriers are mutually orthogonal, or nearly orthogonal. In general, in an OFDM symbol, each subcarrier is independently modulated, often implemented by the inverse discrete Fourier transform (IDFT). In addition, cyclic prefix (CP) is often padded to the transformed data sequence after IDFT. There is a heightened need, in an OFDM-based system, to control power levels of the transmitted signal at which data is communicated. A PAPR (Peak-To-Average Power Ratio) is a power characteristic of the transmitted signal that is of significance in communications in an OFDM-based communication system. In general, a higher PAPR requires the power amplifier (PA) to have a wider linear dynamic range, forces PA to work at a lower average power, which makes the power efficiency lower, costs more electrical energy, reduces battery life, and reduces the service coverage areas.
There is an ongoing need to provide a manner by which to communicate data in an OFDM communication system in which the PAPR of the transmitted signal is of an acceptable level. If, the data that is to be communicated is altered (i.e. processed) in some manner to improve the PAPR, indication of the manner by which the alteration is made often needs to be communicated to the receiving communication station. In many cases such information is needed by the receiving communication station to permit the receiving communication station to make inverse processing for the alteration processing, thereby to facilitate recovery of the informational content of the transmitted data.
One conventional scheme to reduce PAPR, referred to as Partial Transmit Sequence (PTS) scheme, is sometimes utilized. In a Partial Transmit Sequence scheme, for each OFDM symbol of the data that is sent by sending station, additional information also needs to be sent by the sending station to inform the receiving station that receives the communicated data a set of coefficients. Such additional communication, referred to, at times, as side-information (SI), is transmitted, e.g., upon reserved sub-carriers. This need to send separate information on the reserved sub-carriers, or otherwise, is at the expense of bandwidth efficiency. That is to say, bandwidth is required to send the side-information. And, when capacity issues on the reserved sub-carrier, such bandwidth is no longer available for other purposes.
What is needed, therefore, is both a manner by which to place data in a form that leads to improved signal PAPR levels and also a manner by which to provide side information related to the alteration processing of the data into the form leading to the improved PAPR to a receiving station.
It is in light of this background information related to communications in a communication system that utilizes a multi-carrier modulation scheme that the significant improvements of the present invention have evolved.